Feature - Urgency

- Implemented the urgency algorithm according to rfc31.
- Added a new '_urgency' command to test the algorithm.

src/Context.cpp

@@ -249,6 +249,7 @@ int Context::dispatch (std::string &out)
   else if (cmd.command == "_ids")             { rc = handleCompletionIDs         (out); }
   else if (cmd.command == "_config")          { rc = handleCompletionConfig      (out); }
   else if (cmd.command == "_version")         { rc = handleCompletionVersion     (out); }
+  else if (cmd.command == "_urgency")         { rc = handleUrgency               (out); }
   else if (cmd.command == "" &&
            sequence.size ())                  { rc = handleModify                (out); }